Commercial vehicles with automatic transmissions are known in vehicle engineering. The vehicles are used in off-road travel, for example in so-called heavy off-road travel. Such uses are possible for construction site vehicles as well as military vehicles in military deployment. The driving strategy for determining the targeted gear that is assigned to the transmission control or transmission electronics is responsible for finding the optimum gear in each situation. In addition to the weight of the vehicle, the currently predominant vehicle resistance is calculated from physical variables such as the current engine torque and vehicle speed. Extremely high vehicle resistances can arise in off-road travel, for example when embarking on a steep slope or in a bog where the wheels of the commercial vehicle are partially sunken. In these driving situations, sudden downshift into a lower gear is triggered when a shifting rotational speed is reached. The engine rotational speed achieved after shifting can be calculated even before the shifting is triggered based on the change in the transmission ratio and the vehicle resistance that is also active during shifting. This is accomplished by determining the target rotational speed for the chosen targeted gear. The calculated target rotational speed thereby yields an upper target rotational speed limit that may not be exceeded. The driving strategy calculates the maximum gear increment without exceeding the upper target rotational speed limit. Given the transmission ratios, it is possible in extreme situations for very low rotational speeds to result after downshifting in which the engine torque is insufficient for continued driving or the vehicle even stops. This yields a disengaged drivetrain that is unforeseeable by the driver which can cause critical driving situations.
For example in the document DE 10 2004 027 597 A1, a method is known for controlling an automatic transmission during a procedure in which the transmission ratio was changed in which the synchronous rotational speed for the new gear or targeted gear lies below the idle of a drive motor connectable to the transmission, and in which a gear-shifting actuator is activated for engaging the new gear when the gear actuation rotational speed has reached a predefined rotational speed window. In the known method, the shifting operation is performed in an upshifting mode in contrast from the previous downshifting mode.